1. Field of the Invention
The present invention relates to a method of processing a resin sheet or forming ditches on the resin sheet by laser beam radiation and to a resin sheet or part manufactured by such a method. Such a resin sheet is used, for example, as a flexible circuit sheet for making an electrical connection in an instrument panel of an automotive vehicle.
2. Description of Related Art
A method of cutting a resin sheet such as a flexible circuit sheet with a laser beam or forming ditches on a part thereon has been known hitherto. In a conventional method of forming ditches on a resin sheet, as shown in FIG. 7, metal strip 91 is embedded in resin sheet 9 at the bottom of ditch 92 to be formed by laser radiation. A part of the resin where the laser beam is radiated is melt and evaporated, and the laser beam is reflected by metal strip 91 when it reaches metal strip 91 and there the laser beam radiation is stopped, thereby ditch 92 being formed. This method is disclosed in JP-A-2-84282. Another method disclosed in JP-A-2-219651 uses a heat-resistant resin plate in place of the metal strip. To cut partially a resin sheet only at desired positions, a method of controlling the laser beam in an ON and OFF fashion and radiating it intermittently is proposed in JP-A-6-55283.
Both methods disclosed in JP-A-2-84282 and JP-A-2-219651 for making ditches on a resin sheet require an embedded metal strip or heat-resistant plate. The method proposed in JP-A-6-55283 for partially cutting a resin sheet not only requires complex control of the laser beam but also prolongs the processing time. Therefore, productivity in those methods is not high, and accordingly the production cost becomes high.
For manufacturing a flexible circuit sheet, a method in which several flexible circuit sheets are formed on a single sheet and divided into individual circuit sheets by cutting the single sheet with a laser beam is also known. The individual circuit sheets and a part removed from the single sheet as waste are all completely separated in the laser beam processing. Therefore, it is necessary to prepare two conveyor systems to take out separately the circuit sheets as finished products and the sheet part removed as waste in a mass production process. Therefore, the conveyor system becomes complex and expensive.